P,

    It didn't take much searching to find an outfit that sells trepanning
tools.  Here's a picture -- worth the thousand words...?

      BTA Heller Inc. offers its many years of experience with a standard
compliment of indexable trepanning tools to fit the needs of today's
industry.
  The basic principle of trepanning, unlike solid drilling, is that a core
is developed, once the component has been trepanned.  In the majority of
cases, the cores that remain most often can be used to produce other parts.
Trepanning is a great alternative if you don't have sufficient horsepower to
push solid drilling tools.

  We at BTA Heller Inc. can offer trepanning tools to meet most special
needs.  This would include designing trepanning tools that can produce a
specific core size, such as tensile strength sample blanks.  We also offer
mating core cropping tools to make it possible to trepan blind holes.

  Our standard compliment of indexable trepanning tools covers a range of
diameters from 3.500" to 24" and can be threaded for either an internal or
external fast lead thread.  This tooling line is designed with robust
pressed inserts with multiple carbide grades, coatings and chip breakers.
We also offer tools with precision ground inserts for improved chip control
when trepanning specialty materials.  All of our trepanning tools feature
reversible carbide pads for added life and straighter holes.  Our stabilizer
trepan tools are designed with additional carbide nylon guide pads for
improved tool stability to eliminate tool chatter spiraling.


Jack Beale